Butterfly valve is a kind of vale that takes a disc as closing part (butterfly board) which rotates around the valve axis to achieve opening and closing. The valve is mainly for cut-off and throttling on pipeline. Butterfly board is driven by the valve stem. A opening and closing is completed as it rotates 90°. The flow of medium may be controlled by changing of deflection angle of butterfly board. Commonly used butterfly valve includes wafer butterfly valve, lug butterfly valve and flange butterfly valve. Butterfly valve is suitable for pipeline that transports various corrosive, non - corrosive fluids in producer, coal gas, natural gas, liquefied petroleum gas, city gas, hot and cold air, chemical smelting and power environmental protection, building water supply and drainage and other engineering systems for regulating and cut-off of medium flow.